1. Field of the Invention
This invention relates to a printing device of a typewriter or the like, more particularly to the one provided with a mechanism for overprinting either a same character or a different character to a printed character twice or more, so that an attributed character, i.e., a character with a special print effect like a character with an underline or that with a bold face, is printed. The invention further relates to a printing device of a typewriter, specifically, to the one for overprinting characters, those excluding underline and bold face, in spite of being in an underline or bold printing mode, where the character is already underlined or bold.
2. Discussion of Background
One of the prior art English typewriters is well known for having a correction mechanism which erases a word already printed on a printing paper. In the mechanism, a same type as the printed character is hit several times with its position slightly dislocated via a correction tape on which a sticking agent is applied. Accordingly, the printed character formed by an adhesion of the carbon powder is erased because the adhered powder is removed by the agent. In the above correction mechanism, however, the same type is required to be hit twice or more at the same position.
The prior art typewriter with an automatic correction mechanism of another type has been also provided which has a line buffer for storing printed characters by a line. When a print head is moved to a character position to be erased and a correction key is operated, the same type as the printed character is selected based upon the data stored in the line buffer so that the character is erased.
The typewriter of other type has an overprinting mechanism in which another character, either the same as or different from an already printed character, is overprinted at the same position thereof so as to provide more printing possibilities. For example, the aforementioned typewriter has a function of bold printing by typing a same type with its position slightly dislocated twice or more in order to emphasize a certain character. The other typewriter has a function in printing a character part and an underline part at the same position by which a character with underline is printed. Such a complicated function as an overprinting twice or more at the same printing position is automatically executed by a printing device through the operation of a specific key designed for the execution.
In case of erasing the overprinted character, a plurality of erasing operations are executed in such a manner that the character is erased just as it was printed.
The aforementioned printing devices are so constructed that, in the case of printing an attributed character, the attribution is automatically executed by overprinting the attribute part on the character part upon operating the character key together with the key for printing the attributed character. The attribute printing, however, will cause some drawbacks. When an already printed character is required to be attributed, the character part results in being printed twice, since an attributed character is overprinted on the printed character. In case that the print head is out of position even slightly, the width of the character part would be more than other printed characters, causing non-uniformity in the printed characters. Moreover, since at the position where the character is overprinted, a carbon powder of a print ribbon is adhered thicker than that adhered to other parts, the correction ribbon fails to completely remove the carbon powder, resulting in incomplete character erasing.
In a typewriter having a printer with an automatic underline mechanism, for example, the printed character is automatically underlined upon setting an auto underline mode.
In the typewriter with an automatic underline function in case of printing a composite character by overprinting two or more character, e.g., " " with "Y" and "=", in an automatic underline mode, the underline is printed twice or more. Accordingly, the thickness of the underline part would be more than other parts, thereby deteriorating printing quality and requiring more time to print the composite character with the underline, resulting in printing inefficiency and erasure difficulties.